This invention relates to bearings, and more particularly to a class of bearings called thrust bearings. Basically, thrust bearings are characterized in that they separate two flat surfaces that are being pressed together to thereby allow those surfaces to be moved parallel to each other. One thrust bearing for example is described in U.S. Pat. No. 2,609,674 issued Sept. 7, 1952. Thrust bearings are to be distinguished from other types of bearings, such as shaft support bearings. An exemplary shaft support bearing is described in U.S. Pat. No. 718,376 issued Jan. 13, 1903. Basically, shaft support bearings extend around the circumference of a shaft to allow it to rotate while being held in a particular axial alignment.
In the prior art, thrust bearings were either of the two-point contact type, or of the four-point contact type. The former have only one contact point with each of the two flat surfaces that they separate; whereas the latter have two contact points with each of the surfaces that they separate. Four-point contact bearings are preferred because they can withstand greater compressing forces between the flat surfaces. By definition, average stress at a contact point in a thrust bearing equals the compressing force between the flat surfaces divided by the contact area. And in general, the contact area in a four-point contact thrust bearing is larger then that of two-point contact thrust bearing.
However, inspite of their ability to withstand high compressing forces, four-point contact thrust bearings have in the past received substantially less use than two-point contact thrust bearings. A primary reason for this is that prior art four-point contact thrust bearings would wear due to slippage that occurred at the contact points between the balls and the raceways of the bearing. By comparison, two-point contact thrust bearing simply do not have this problem.
Therefore, the primary object of the present invention is to provide a four-point contact thrust bearing which also has zero slippage between its balls and raceway.